1. Field of the Invention
The present invention relates to a method of recording color video signals and particularly to a method of recording broad-band color video signals and a digital audio signal on the basis of superimposition on recording media. The present invention also relates to a method of recording and reproducing broad band color video signals for HDTV (high definition television) broadcasting.
2. Description of Background Information
As a recording medium on which a color video signal and a digital audio signal are recorded, there is commercialized a "Hi-Fi Video Disc" on which are recorded the conventional video disc recording signal and in addition a digital audio signal in a so-called "CD (Compact Disc) format" in the manner of superimposition.
With this Hi-Fi video disc, dynamic range of the digital audio signal can be raised as high as 90 db or more, thereby significantly improving the sound quality as compared with the audio signal recording-playback system based on the frequency modulation method. On the other hand, however, the video band is determined by the width of side band of the FM video signal, and of the video band is made too wide, the reproduced video signal and analog audio signal are adversely affected by the interference between the side band of the FM video signal and the analog audio carrier signal. On this account, it is not possible to set the band of video signal to 4.2 MHz or higher, and therefore the resolution of picture is restricted.
A conceivable breakthrough is to eliminate the FM audio signal components, leaving only the digital audio signal component. This scheme enables recording of a video signal having a band width of 6 MHz, and the picture resolution can be improved.
Even with this recording method, however, it is not possible to record a broad-band color video signal of HDTV broadcasting. Namely, the broad-band color video signals for HDTV broadcasting has a band width five times (20 MHz) the color video signal of the NTSC system. Therefore, it can not be processed even by means of a recording system with a 6 MHz band width. Thus, the broad-band color video signal for HDTV broadcasting can not be recorded on an optical video disc by means of the conventional recording/playback method oriented to video signals with the band width below 6 MHz.
With the intention of recording the broad-band color video signal for HDTV broadcasting on the optical recording disc, a recording method is conceivable in which the recording disc is rotated at a high speed. In this method, however, the disc speed is as high as 6000 rpm, and it is difficult to design a focus servo system for focusing the information reading laser bean on the recording surface of the recording disc and a tracking servo system for positioning the spot of the information reading laser beam formed on the surface of the recording disc. It is also difficult to have a long time continuous playback by the broad-band color video signals.
Another method has been proposed, in which the broad-band color video signal is compressed in band width by the MUSE (Multiple Sub-Nyquist Sampling Encoding) system, and the band-compressed color video signal is recorded and reproduced with the conventional signal write and read units. The MUSE system, however, has a drawback of deterioration of resolution for moving pictures.